Organosilicon-modified polyimide resin composition and use thereof

ABSTRACT

wherein Ar1 is a tetra-valent organic group having a benzene ring or an alicyclic hydrocarbon structure, Ar2 is a di-valent organic group, R is each independently methyl or phenyl, and the thermal curing agent is selected from the group consisting of epoxy resin, isocyanate and bisoxazoline compounds. The resultant organosilicon-modified polyimide resin composition of the present disclosure has superior transmittance, heat resistance and mechanical strength, and is suitable for producing a flexible LED filament.

BACKGROUND Technical Field

The present disclosure relates the field of illumination, andspecifically to an organosilicon-modified polyimide resin composition.

Description of Related Art

LED is gradually replacing conventional illuminating devices due to itsadvantages such as environmental friendliness, energy saving, highefficiency and long lifespan. However, the light emitted by conventionalLED light resources is directional, and wide angle illumination cannotbe achieved as can be done by conventional illuminating devices. Inrecent years, filaments which make LED light resources achieve 360°omnidirectional illumination similar to that can be done by conventionaltungsten lamps has drawn great attention.

Patent Publication No. CN103994349A discloses an LED lamp with highluminous efficiency, wherein a plurality of LED chips are fixed on atransparent substrate which comprises filament electrodes at both ends.The material for the transparent substrate may be transparent glass,microcrystalline glass, transparent ceramic, yttrium aluminum garnet,alumina (sapphire), chlorine oxynitride, yttrium oxide ceramic, calciumoxide ceramic or transparent heat-resistant PC/PS/PMMA. Although theloss of blue light caused by the downward blue light emitted by the LEDchip being reflected and passing through the P-N junction can be avoidedby using this transparent substrate, the substrate is a hard one whichcannot be bent and therefore has a disadvantage of narrow illuminatingangle.

Patent Publication No. CN204289439U discloses an LED filament whichprovides omnidirectional illumination, which comprises a substratehaving fluorescent powders mixed therein, an electrode disposed on thesubstrate, at least one LED chip mounted on the substrate, and apackaging adhesive covering the LED chip. By the substrate formed from asilicone resin comprising fluorescent powders, the cost of making thesubstrate from glass or sapphire is eliminated. The filament made fromsaid substrate avoids the effect of glass or sapphire on the lightemission of the chip, achieves 360° light emission, and significantlyimproves the emission uniformity and the luminous efficiency. However,as the substrate is formed from silicone resin, it has the disadvantageof poor heat-resistance.

The present application makes further optimization to the aboveapplications, so as to further meet various process requirements.

SUMMARY

The main technical problem to be addressed by the present disclosure isto provide a composition used for a filament substrate or alight-conversion layer to effectively improve the properties of thecurrently available substrates, such as heat resistance, thermalconductivity, tensile strength and filament performance.

The present disclosure provides a composition which is suitable for useas a filament substrate or a light-conversion layer, wherein thecomposition comprises at least a main material, a modifier and anadditive. The main material is an organosilicon-modified polyimide; themodifier is a thermal curing agent; and the additive comprisesmicroparticles added into the main material, which may comprisefluorescent powders and heat dispersing particles. The additive may alsocomprise a coupling agent.

The present disclosure provides a composition which is suitable for useas a filament substrate or a light-conversion layer, wherein the mainmaterial in the composition is an organosilicon-modified polyimide, i.e.a polyimide comprising a siloxane moiety, wherein theorganosilicon-modified polyimide comprises a repeating unit representedby general formula (I):

In general formula (I), Ar¹ is a tetra-valent organic group having abenzene ring or an alicyclic hydrocarbon structure, Ar² is a di-valentorganic group, R is each independently methyl or phenyl, and n is 1˜5.

According to an embodiment of the present disclosure, Ar¹ is atetra-valent organic group having a monocyclic alicyclic hydrocarbonstructure or a bridged-ring alicyclic hydrocarbon structure.

According to another embodiment of the present disclosure, Ar² is adi-valent organic group having a monocyclic alicyclic hydrocarbonstructure.

According to another embodiment of the present disclosure, Ar¹ is atetra-valent organic group having a benzene ring or an alicyclichydrocarbon structure comprising a functional group having activehydrogen, wherein the functional group having active hydrogen is any oneof hydroxyl, amino, carboxy and mercapto.

According to another embodiment of the present disclosure, Ar² is adi-valent organic group comprising a functional group having activehydrogen, wherein the functional group having active hydrogen is any oneof hydroxyl, amino, carboxy and mercapto.

According to another embodiment of the present disclosure, Ar¹ in theorganosilicon-modified polyimide is derived from a dianhydride, and Ar²is derived from a diamine.

According to another embodiment of the present disclosure, the molarpercentage of the diamine comprising a functional group having activehydrogen is 5˜25% of the total amount of diamine.

According to another embodiment of the present disclosure, the siloxanecontent in the organosilicon-modified polyimide is 20˜75 wt %.

According to another embodiment of the present disclosure, the siloxanecontent in the organosilicon-modified polyimide is 30˜70 wt %, and theglass transition temperature is below 150° C.

According to another embodiment of the present disclosure, the numberaverage molecular weight of the organosilicon-modified polyimide is5000˜60000, preferably 10000˜40000.

According to another embodiment of the present disclosure, the weight ofthe heat dispersing particles is 1˜12 times the weight of theorganosilicon-modified polyimide.

The present disclosure provides a composition which is suitable for useas a filament substrate or a light-conversion layer, wherein themodifier in the composition is a thermal curing agent which is selectedfrom the group consisting of epoxy resin, isocyanate and bisoxazolinecompounds.

According to another embodiment of the present disclosure, the molarratio of the thermal curing agent to the functional group having activehydrogen in the organosilicon-modified polyimide is 1:1.

The present disclosure provides a composition which is suitable for useas a filament substrate or a light-conversion layer, wherein theadditive in the composition may comprise fluorescent powders, heatdispersing particles and a coupling agent.

According to another embodiment of the present disclosure, the heatdispersing particles are one or more selected from the group consistingof silica, alumina, magnesium oxide, magnesium carbonate, aluminumnitride, boron nitride and diamond.

According to another embodiment of the present disclosure, the heatdispersing particles have an average particle size of from 0.1 μm to 100μm, preferably from 1 μm to 50 μm.

According to another embodiment of the present disclosure, thefluorescent powders are at least one of red fluorescent powders, yellowfluorescent powders and green fluorescent powders.

According to another embodiment of the present disclosure, thefluorescent powders have spherical, plate or needle shape.

According to another embodiment of the present disclosure, thefluorescent powders have an average particle size of above 0.1 μm;preferably from 1 μm to 100 μm; more preferably from 1 to 50 μm.

According to another embodiment of the present disclosure, the weightratio of the fluorescent powders to the organosilicon-modified polyimideis 50˜800:100, preferably 100˜700:100.

According to another embodiment of the present disclosure, thecomposition further comprises one or more of a defoaming agent, aleveling agent and an adhesive.

The present disclosure provides a composition which is suitable for useas a filament substrate or a light-conversion layer, wherein theadditive in the composition may comprise fluorescent powders and heatdispersing particles, wherein the heat dispersing particles have aparticle size distribution of 0.1˜100 μm, and the content of smallparticle size (below 1 μm) is about 5-20%, the content of mediumparticle size (1-30 μm) is about 50-70%, and the content of largeparticle size (above 30 μm) is about 20-40%.

According to another embodiment of the present disclosure, the amount ofthe fluorescent powders is no less than 0.05 times, preferably not lessthan 0.1 times, and no more than 8 time, preferably no more than 7times, the weight of the organosilicon-modified polyimide.

According to another embodiment of the present disclosure, the weight ofthe heat dispersing particles is 1˜12 times the weight of theorganosilicon-modified polyimide.

Another aspect of the present disclosure provides a filament substrateor a light-conversion layer formed from the above organosilicon-modifiedpolyimide composition, wherein the filament substrate or thelight-conversion layer has a thermal conductivity of more than 1.8W/m*K.

According to another embodiment of the present disclosure, the siloxanecontent in the organosilicon-modified polyimide composition is 20˜75 wt%.

According to another embodiment of the present disclosure, the weight ofthe heat dispersing particles contained in the organosilicon-modifiedpolyimide composition is 1˜12 times the weight of theorganosilicon-modified polyimide.

Another aspect of the present disclosure provides a filament substrateor a light-conversion layer formed from the above organosilicon-modifiedpolyimide composition, wherein the filament substrate or thelight-conversion layer has an elastic modulus of more than 2.0 GPa.

According to another embodiment of the present disclosure, the siloxanecontent in the organosilicon-modified polyimide composition is 20˜75 wt%.

According to another embodiment of the present disclosure, the weight ofthe heat dispersing particles contained in the organosilicon-modifiedpolyimide composition is 1˜12 times the weight of theorganosilicon-modified polyimide.

Another aspect of the present disclosure provides a filament substrateor a light-conversion layer formed from the above organosilicon-modifiedpolyimide composition, wherein the filament substrate or thelight-conversion layer has an elongation at break of more than 0.5%.

According to another embodiment of the present disclosure, the siloxanecontent in the organosilicon-modified polyimide composition is 20˜75 wt%.

According to another embodiment of the present disclosure, the weight ofthe heat dispersing particles contained in the organosilicon-modifiedpolyimide composition is 1˜12 times the weight of theorganosilicon-modified polyimide.

Another aspect of the present disclosure provides a filament substrateor a light-conversion layer formed from the above composition.

Comparing with the prior art, the present disclosure achieves one ormore of the following advantages:

a) Using the organosilicon-modified polyimide as the body, theorganosilicon-modified polyimide resin composition formed by adding athermal curing agent has excellent heat resistance, mechanical strengthand transparency;b) Using the organosilicon-modified polyimide resin composition as thefilament substrate, the filament has good flexibility, so that thefilament can be made into various shapes to achieve 360° omnidirectionalillumination; andc) The amidation is carried out by vacuum defoaming or in a nitrogenatmosphere, so that the volumetric percentage of cells in theorganosilicon-modified polyimide is 5˜20%; accordingly, the lightemission is more uniform after the light emitted by the LED chip isrefracted by the cells.

The present disclosure further provides a modification method, in whichthe properties of the filament substrate or the light-conversion layercan be modified by adjusting the type and the content of one or more ofthe main material, the modifier (thermal curing agent) and the additivein the organosilicon-modified polyimide, so as to meet specialenvironmental requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the TMA analysis of the polyimide before and after addingthe thermal curing agent.

FIG. 2 shows the particle size distributions of the heat dispersingparticles with different specifications.

FIG. 3 shows the SEM image of an organosilicon-modified polyimide resincomposition composite film (substrate).

FIG. 4a shows the cross-sectional scheme of an organosilicon-modifiedpolyimide resin composition composite film (substrate) according to anembodiment of the present disclosure.

FIG. 4b shows the cross-sectional scheme of an organosilicon-modifiedpolyimide resin composition composite film (substrate) according toanother embodiment of the present disclosure.

FIG. 5 shows the perspective partially sectioned scheme of an LEDfilament according to an embodiment of the present disclosure.

FIG. 6 shows the cross-sectional scheme of the layered structure of afilament according to an embodiment of the present disclosure.

FIG. 7 shows the perspective scheme of an LED bulb according to thepresent disclosure.

DETAILED DESCRIPTION

The material suitable for manufacturing a filament substrate or alight-conversion layer for LED should have properties such as excellentlight transmission, good heat resistance, excellent thermalconductivity, appropriate refraction rate, excellent mechanicalproperties and good warpage resistance. All the above properties can beachieved by adjusting the type and the content of the main material, themodifier and the additive contained in the organosilicon-modifiedpolyimide composition. The present disclosure provides a filamentsubstrate or a light-conversion layer formed from a compositioncomprising an organosilicon-modified polyimide. The composition can meetthe requirements on the above properties. In addition, the type and thecontent of one or more of the main material, the modifier (thermalcuring agent) and the additive in the composition can be modified toadjust the properties of the filament substrate or the light-conversionlayer, so as to meet special environmental requirements. Themodification of each property is described herein below.

Adjustment of the Organosilicon-Modified Polyimide

The organosilicon-modified polyimide provided herein comprises arepeating unit represented by the following general formula (I):

In general formula (I), Ar¹ is a tetra-valent organic group. The organicgroup has a benzene ring or an alicyclic hydrocarbon structure. Thealicyclic hydrocarbon structure may be monocyclic alicyclic hydrocarbonstructure or a bridged-ring alicyclic hydrocarbon structure, which maybe a dicyclic alicyclic hydrocarbon structure or a tricyclic alicyclichydrocarbon structure. The organic group may also be a benzene ring oran alicyclic hydrocarbon structure comprising a functional group havingactive hydrogen, wherein the functional group having active hydrogen isone or more of hydroxyl, amino, carboxy, amido and mercapto.

Ar² is a di-valent organic group, which organic group may have forexample a monocyclic alicyclic hydrocarbon structure or a di-valentorganic group comprising a functional group having active hydrogen,wherein the functional group having active hydrogen is one or more ofhydroxyl, amino, carboxy, amido and mercapto.

R is each independently methyl or phenyl.

n is 1˜5, preferably 1, 2, 3 or 5.

The polymer of general formula (I) has a number average molecular weightof 5000˜100000, preferably 10000˜60000, more preferably 20000˜40000. Thenumber average molecular weight is determined by gel permeationchromatography (GPC) and calculated based on a calibration curveobtained by using standard polystyrene. When the number averagemolecular weight is below 5000, a good mechanical property is hard to beobtained after curing; especially the elongation tends to decrease. Onthe other hand, when it exceeds 100000, the viscosity becomes too highand the resin is hard to be formed.

Ar¹ is a moiety derived from a dianhydride, which may be an aromaticanhydride or an aliphatic anhydride. The aromatic anhydride includes anaromatic anhydride comprising only a benzene ring, a fluorinatedaromatic anhydride, an aromatic anhydride comprising amido group, anaromatic anhydride comprising ester group, an aromatic anhydridecomprising ether group, an aromatic anhydride comprising sulfide group,an aromatic anhydride comprising sulfonyl group, and an aromaticanhydride comprising carbonyl group.

Examples of the aromatic anhydride comprising only a benzene ringinclude pyromellitic dianhydride (PMDA), 2,3,3′,4′-biphenyltetracarboxylic dianhydride (aBPDA), 3,3′,4,4′-biphenyl tetracarboxylicdianhydride (sBPDA), and4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA). Examples of thefluorinated aromatic anhydride include4,4′-(hexafluoroisopropylidene)diphthalic anhydride which is referred toas 6FDA. Examples of the aromatic anhydride comprising amido groupincludeN,N′-(5,5′-(perfluoropropane-2,2-diyl)bis(2-hydroxy-5,1-phenylene))bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxamide)(6FAP-ATA), andN,N′-(9H-fluoren-9-ylidenedi-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide] (FDA-ATA). Examples of the aromatic anhydride comprisingester group include p-phenylene bis(trimellitate)dianhydride (TAHQ).Examples of the aromatic anhydride comprising ether group include4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA),4,4′-oxydiphthalic dianhydride (sODPA), and 2,3,3′,4′-diphenyl ethertetracarboxylic dianhydride (aODPA). Examples of the aromatic anhydridecomprising sulfide group include 4,4′-bis(phthalic anhydride)sulfide(TPDA). Examples of the aromatic anhydride comprising sulfonyl groupinclude 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA).Examples of the aromatic anhydride comprising carbonyl group include3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA).

The alicyclic anhydride includes 1,2,4,5-cyclohexanetetracarboxylic aciddianhydride which is referred to as HPMDA, 1,2,3,4-butanetetracarboxylicdianhydride (BDA),tetrahydro-1H-5,9-methanopyrano[3,4-d]oxepine-1,3,6,8(4H)-tetrone (TCA),hexahydro-4,8-ethano-1H,3H-benzo[1,2-C:4,5-C′]difuran-1,3,5,7-tetrone(BODA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), and1,2,3,4-cyclopentanetetracarboxylic dianhydride (CpDA); or alicyclicanhydride comprising an olefin structure, such asbicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (COeDA).When an anhydride comprising ethynyl such as4,4′-(ethyne-1,2-diyl)diphthalic anhydride (EBPA) is used, themechanical strength of the light-conversion layer can be further ensuredby post-curing.

Considering the solubility, 4,4′-oxydiphthalic anhydride (sODPA),3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), cyclobutanetetracarboxylic dianhydride (CBDA) and4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) arepreferred. The above dianhydride can be used alone or in combination.

Ar² is derived from diamine which may be an aromatic diamine or analiphatic diamine. The aromatic diamine includes an aromatic diaminecomprising only a benzene ring, a fluorinated aromatic diamine, anaromatic diamine comprising ester group, an aromatic diamine comprisingether group, an aromatic diamine comprising amido group, an aromaticdiamine comprising carbonyl group, an aromatic diamine comprisinghydroxyl group, an aromatic diamine comprising carboxy group, anaromatic diamine comprising sulfonyl group, and an aromatic diaminecomprising sulfide group.

The aromatic diamine comprising only a benzene ring includesm-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene,2,6-diamino-3,5-diethyltoluene, 3,3′-dimethylbiphenyl-4,4′-diamine,9,9-bis(4-aminophenyl)fluorene (FDA),9,9-bis(4-amino-3-methylphenyl)fluorene, 2,2-bis(4-aminophenyl)propane,2,2-bis(3-methyl-4-aminophenyl)propane,4,4′-diamino-2,2′-dimethylbiphenyl (APB). The fluorinated aromaticdiamine includes 2,2′-bis(trifluoromethyl) benzidine (TFMB),2,2-bis(4-aminophenyl)hexafluoropropane (6FDAM),2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), and2,2-bis(3-amino-4-methylphenyl) hexafluoropropane (BIS-AF-AF). Thearomatic diamine comprising ester group includes[4-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate (ABHQ),bis(4-aminophenyl)terephthalate (BPTP), and 4-aminophenyl4-aminobenzoate (APAB). The aromatic diamine comprising ether groupincludes 2,2-bis[4-(4-aminophenoxy)phenyl]propane) (BAPP),2,2′-bis[4-(4-aminophenoxy) phenyl]propane (ET-BDM),2,7-bis(4-aminophenoxy)-naphthalene (ET-2,7-Na),1,3-bis(3-aminophenoxy)benzene (TPE-M),4,4′-[1,4-phenyldi(oxy)]bis[3-(trifluoromethyl)aniline] (p-6FAPB),3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether (ODA),1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene(TPE-Q), and 4,4′-bis(4-aminophenoxy)biphenyl (BAPB). The aromaticdiamine comprising amido group includesN,N′-bis(4-aminophenyl)benzene-1,4-dicarboxamide (BPTPA),3,4′-diaminobenzanilide (m-APABA), and 4,4′-diaminobenzanilide (DABA).The aromatic diamine comprising carbonyl group includes4,4′-diaminobenzophenone (4,4′-DABP), and bis(4-amino-3-carboxyphenyl)methane (or referred to as 6,6′-diamino-3,3′-methylenediyl-dibenzoicacid). The aromatic diamine comprising hydroxyl group includes3,3′-dihydroxybenzidine (HAB), and2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP). The aromaticdiamine comprising carboxy group includes6,6′-diamino-3,3′-methylenedibenzoic acid (MBAA), and 3,5-diaminobenzoicacid (DBA). The aromatic diamine comprising sulfonyl group includes3,3′-diaminodiphenylsulfone (DDS), 4,4′-diaminodiphenylsulfone,bis[4-(4-aminophenoxy)phenyl] sulfone (BAPS) (or referred to as4,4′-bis(4-aminophenoxy)diphenylsulfone), and3,3′-diamino-4,4′-dihydroxydiphenylsulfone (ABPS). The aromatic diaminecomprising sulfide group includes 4,4′-diaminodiphenyl sulfide.

The aliphatic diamine is a diamine which does not comprise any aromaticstructure (e.g., benzene ring). The aliphatic diamine includesmonocyclic alicyclic amine and straight chain aliphatic diamine, whereinthe straight chain aliphatic diamine include siloxane diamine, straightchain alkyl diamine and straight chain aliphatic diamine comprisingether group. The monocyclic alicyclic diamine includes4,4′-diaminodicyclohexylmethane (PACM), and3,3′-dimethyl-4,4-diaminodicyclohexylmethane (DMDC). The siloxanediamine (or referred to as amino-modified silicone) includesα,ω-(3-aminopropyl)polysiloxane (KF8010), X22-161A, X22-161B, NH15D, and1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (PAME). Thestraight chain alkyl diamine has 6˜12 carbon atoms, and is preferablyun-substituted straight chain alkyl diamine. The straight chainaliphatic diamine comprising ether group includes ethylene glycoldi(3-aminopropyl) ether.

The diamine can also be a diamine comprising fluorenyl group. Thefluorenyl group has a bulky free volume and rigid fused-ring structure,which renders the polyimide good heat resistance, thermal and oxidationstabilities, mechanical properties, optical transparency and goodsolubility in organic solvents. The diamine comprising fluorenyl group,such as 9,9-bis(3,5-difluoro-4-aminophenyl)fluorene, may be obtainedthrough a reaction between 9-fluorenone and 2,6-dichloroaniline. Thefluorinated diamine can be 1,4-bis(3′-amino-5′-trifluoromethylphenoxy)biphenyl, which is a meta-substituted fluorine-containing diamine havinga rigid biphenyl structure. The meta-substituted structure can hinderthe charge flow along the molecular chain and reduce the intermolecularconjugation, thereby reducing the absorption of visible lights. Usingasymmetric diamine or anhydride can increase to some extent thetransparency of the organosilicon-modified polyimide resin composition.The above diamines can be used alone or in combination.

Examples of diamines having active hydrogen include diamines comprisinghydroxyl group, such as 3,3′-diamino-4,4′-dihydroxybiphenyl,4,4′-diamino-3,3′-dihydroxy-1,1′-biphenyl (or referred to as3,3′-dihydroxybenzidine) (HAB), 2,2-bis(3-amino-4-hydroxyphenyl)propane(BAP), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP),1,3-bis(3-hydroxy-4-aminophenoxy) benzene,1,4-bis(3-hydroxy-4-aminophenyl)benzene and3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). Examples of diaminescomprising carboxy group include 3,5-diaminobenzoic acid,bis(4-amino-3-carboxyphenyl)methane (or referred to as6,6′-diamino-3,3′-methylenedibenzoic acid),3,5-bis(4-aminophenoxy)benzoic acid, and1,3-bis(4-amino-2-carboxyphenoxy)benzene. Examples of diaminescomprising amino group include 4,4′-diaminobenzanilide (DABA),2-(4-aminophenyl)-5-aminobenzoimidazole, diethylenetriamine,3,3′-diaminodipropylamine, triethylenetetramine, andN,N′-bis(3-aminopropyl)ethylenediamine (or referred to asN,N-di(3-aminopropyl)ethylethylamine). Examples of diamines comprisingmercapto group include 3,4-diaminobenzenethiol. The above diamines canbe used alone or in combination.

The organosilicon-modified polyimide can be synthesized by well-knownsynthesis methods. For example, it can be prepared from a dianhydrideand a diamine which are dissolved in an organic solvent and subjected toimidation in the presence of a catalyst. Examples of the catalystinclude acetic anhydride/triethylamine, and valerolactone/pyridine.Preferably, removal of water produced in the azeotropic process in theimidation is promoted by using a dehydrant such as toluene.

Polyimide can also be obtained by carrying out an equilibrium reactionto give a poly(amic acid) which is heated to dehydrate. In otherembodiments, the polyimide backbone may have a small amount of amicacid. For example, the ratio of amic acid to imide in the polyimidemolecule may be 1˜3:100. Due to the interaction between amic acid andthe epoxy resin, the substrate has superior properties. In otherembodiments, a solid state material such as a thermal curing agent,inorganic heat dispersing particles and fluorescent powders can also beadded at the state of poly(amic acid) to give the substrate. Inaddition, solubilized polyimide can also be obtained by direct heatingand dehydration after mixing alicylic anhydride and diamine. Suchsolubilized polyimide, as an adhesive material, has a good lighttransmittance. In addition, it is liquid state; therefore, other solidmaterials (such as the inorganic heat dispersing particles and thefluorescent powders) can be dispersed in the adhesive material moresufficiently.

In one embodiment for preparing the organosilicon-modified polyimide,the organosilicon-modified polyimide can be produced by dissolving thepolyimide obtained by heating and dehydration after mixing a diamine andan anhydride and a siloxane diamine in a solvent. In another embodiment,the amidic acid, before converting to polyimide, is reacted with thesiloxane diamine.

In addition, the polyimide compound may be obtained by dehydration andring-closing and condensation polymerization from an anhydride and adiamine, such as an anhydride and a diamine in a molar ratio of 1:1. Inone embodiment, 200 micromole (mmol) of4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 20 micromole(mmol) of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 50micromole (mmol) of 2,2′-di(trifluoromethyl)diaminobiphenyl (TFMB) and130 micromole (mmol) of aminopropyl-terminated poly(dimethylsiloxane)are used to give the PI synthesis solution.

The above methods can be used to produce amino-terminated polyimidecompounds.

However, other methods can be used to produce carboxy-terminatedpolyimide compounds. In addition, in the above reaction betweenanhydride and diamine, where the backbone of the anhydride comprises acarbon-carbon triple bond, the affinity of the carbon-carbon triple bondcan promote the molecular structure. Alternatively, a diamine comprisingvinyl siloxane structure can be used.

The molar ratio of dianhydride to diamine may be 1:1. The molarpercentage of the diamine comprising a functional group having activehydrogen may be 5˜25% of the total amount of diamine. The temperatureunder which the polyimide is synthesized is preferably 80˜250° C., morepreferably 100˜200° C. The reaction time may vary depending on the sizeof the batch. For example, the reaction time for obtaining 10˜30 gpolyimide is 6˜10 hours.

The organosilicon-modified polyimide can be classified as fluorinatedaromatic organosilicon-modified polyimides and aliphaticorganosilicon-modified polyimides. The fluorinated aromaticorganosilicon-modified polyimides are synthesized from siloxane-typediamine, aromatic diamine comprising fluoro (F) group (or referred to asfluorinated aromatic diamine) and aromatic dianhydride comprising fluoro(F) group (or referred to as fluorinated aromatic anhydride). Thealiphatic organosilicon-modified polyimides are synthesized fromdianhydride, siloxane-type diamine and at least one diamine notcomprising aromatic structure (e.g., benzene ring) (or referred to asaliphatic diamine), or from diamine (one of which is siloxane-typediamine) and at least one dianhydride not comprising aromatic structure(e.g., benzene ring) (or referred to as aliphatic anhydride). Thealiphatic organosilicon-modified polyimide includes semi-aliphaticorganosilicon-modified polyimide and fully aliphaticorganosilicon-modified polyimide. The fully aliphaticorganosilicon-modified polyimide is synthesized from at least onealiphatic dianhydride, siloxane-type diamine and at least one aliphaticdiamine. The raw materials for synthesizing the semi-aliphaticorganosilicon-modified polyimide include at least one aliphaticdianhydride or aliphatic diamine. The raw materials required forsynthesizing the organosilicon-modified polyimide and the siloxanecontent in the organosilicon-modified polyimide would have certaineffects on transparency, chromism, mechanical property, warpage extentand refractivity of the substrate.

The organosilicon-modified polyimide of the present disclosure has asiloxane content of 20˜75 wt %, preferably 30˜70 wt %, and a glasstransition temperature of below 150° C. The glass transition temperature(Tg) is determined on TMA-60 manufactured by Shimadzu Corporation afteradding a thermal curing agent to the organosilicon-modified polyimide.The determination conditions include: load: 5 gram; heating rate: 10°C./min; determination environment: nitrogen atmosphere; nitrogen flowrate: 20 ml/min; temperature range: −40 to 300° C. When the siloxanecontent is below 20%, the film prepared from the organosilicon-modifiedpolyimide resin composition may become very hard and brittle due to thefilling of the fluorescent powders and thermal conductive fillers, andtend to warp after drying and curing, and therefore has a lowprocessability. In addition, its resistance to thermochromism becomeslower. On the other hand, when the siloxane content is above 75%, thefilm prepared from the organosilicon-modified polyimide resincomposition becomes opaque, and has reduced transparency and tensilestrength. Here, the siloxane content is the weight ratio ofsiloxane-type diamine (having a structure shown in formula (A)) to theorganosilicon-modified polyimide, wherein the weight of theorganosilicon-modified polyimide is the total weight of the diamine andthe dianhydride used for synthesizing the organosilicon-modifiedpolyimide subtracted by the weight of water produced during thesynthesis.

wherein R is methyl or phenyl, preferably methyl, n is 1˜5, preferably1, 2, 3 or 5.

The only requirements on the organic solvent used for synthesizing theorganosilicon-modified polyimide are to dissolve theorganosilicon-modified polyimide and to ensure the affinity(wettability) to the fluorescent powders or the fillers to be added.However, excessive residue of the solvent in the product should beavoided. Normally, the number of moles of the solvent is equal to thatof water produced by the reaction between diamine and anhydride. Forexample, 1 mol diamine reacts with 1 mol anhydride to give 1 mol water;then the amount of solvent is 1 mol. In addition, the organic solventused has a boiling point of above 80° C. and below 300° C., morepreferably above 120° C. and below 250° C., under standard atmosphericpressure. Since drying and curing under a lower temperature are neededafter coating, if the temperature is lower than 120° C., good coatingcannot be achieved due to high drying speed during the coating process.If the boiling point of the organic solvent is higher than 250° C., thedrying under a lower temperature may be deferred. Specifically, theorganic solvent may be an ether-type organic solvent, an ester-typeorganic solvent, a dimethylether-type organic solvent, a ketone-typeorganic solvent, an alcohol-type organic solvent, an aromatichydrocarbon solvent or other solvents. The ether-type organic solventincludes ethylene glycol monomethyl ether, ethylene glycol monoethylether, propylene glycol monomethyl ether, propylene glycol monoethylether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether,ethylene glycol dibutyl ether, diethylene glycol dimethyl ether,diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether,dipropylene glycol dimethyl ether or diethylene glycol dibutyl ether,and diethylene glycol butyl methyl ether. The ester-type organic solventincludes acetates, including ethylene glycol monoethyl ether acetate,diethylene glycol monobutyl ether acetate, propylene glycol monomethylether acetate, propyl acetate, propylene glycol diacetate, butylacetate, isobutyl acetate, 3-methoxybutyl acetate,3-methyl-3-methoxybutyl acetate, benzyl acetate and2-(2-butoxyethoxy)ethyl acetate; and methyl lactate, ethyl lactate,n-butyl acetate, methyl benzoate and ethyl benzoate. The dimethylether-type solvent includes triethylene glycol dimethyl ether andtetraethylene glycol dimethyl ether. The ketone-type solvent includesacetylacetone, methyl propyl ketone, methyl butyl ketone, methylisobutyl ketone, cyclopentanone, and 2-heptanone. The alcohol-typesolvent includes butanol, isobutanol, isopentanol, 4-methyl-2-pentanol,3-methyl-2-butanol, 3-methyl-3-methoxybutanol, and diacetonealcohol. Thearomatic hydrocarbon solvent includes toluene and xylene. Other solventsinclude γ-butyrolactone, N-methylpyrrolidone, N,N-dimethylformamide,N,N-dimethylacetamide and dimethylsulfoxide.

The present disclosure provides an organosilicon-modified polyimideresin composition comprising the above organosilicon-modified polyimideand a thermal curing agent, which may be epoxy resin, isocyanate orbisoxazoline compound. In one embodiment, based on the weight of theorganosilicon-modified polyimide, the amount of the thermal curing agentis 5˜12% of the weight of the organosilicon-modified polyimide. Theorganosilicon-modified polyimide resin composition may further compriseheat dispersing particles and fluorescent powders.

Light Transmittance

The factors affecting the light transmittance of theorganosilicon-modified polyimide resin composition at least include thetype of the main material, the type of the modifier (thermal curingagent), the type and content of the heat dispersing particles, and thesiloxane content. Light transmittance refers to the transmittance of thelight near the main light-emitting wavelength range of the LED chip. Forexample, blue LED chip has a main light-emitting wavelength of around450 nm, then the composition or the polyimide should have low enough oreven no absorption to the light having a wavelength around 450 nm, so asto ensure that most or even all the light can pass through thecomposition or the polyimide. In addition, when the light emitted by theLED chip passes through the interface of two materials, the closer therefractive indexes of the two materials, the higher the light outputefficiency. In order to be close to the refractive index of the material(such as die bonding glue) contacting with the filament substrate (orbase layer), the organosilicon-modified polyimide composition has arefractive index of 1.4˜1.7, preferably 1.4˜1.55. In order to use theorganosilicon-modified polyimide resin composition as a substrate in thefilament, the organosilicon-modified polyimide resin composition isrequired to have good light transmittance at the peak wavelength ofInGaN of the blue-excited white LED. In order to obtain a goodtransmittance, the raw materials for synthesizing theorganosilicon-modified polyimide, the thermal curing agent and the heatdispersing particles can be adjusted. Because the fluorescent powders inthe organosilicon-modified polyimide resin composition may have certaineffect on the transmittance test, the organosilicon-modified polyimideresin composition used for the transmittance test does not comprisefluorescent powders. Such an organosilicon-modified polyimide resincomposition has a transmittance of 86˜93%, preferably 88˜91%, orpreferably 89˜92%, or preferably 90˜93%.

In the reaction of anhydride and diamine to produce polyimide, theanhydride and the diamine may vary. In other words, the polyimidesproduced from different anhydrides and different diamines may havedifferent light transmittances. The aliphatic organosilicon-modifiedpolyimide resin composition comprises the aliphaticorganosilicon-modified polyimide and the thermal curing agent, while thefluorinated aromatic organosilicon-modified polyimide resin compositioncomprises the fluorinated aromatic organosilicon-modified polyimide andthe thermal curing agent. Since the aliphatic organosilicon-modifiedpolyimide has an alicyclic structure, the aliphaticorganosilicon-modified polyimide resin composition has a relatively highlight transmittance. In addition, the fluorinated aromatic,semi-aliphatic and full aliphatic polyimides all have good lighttransmittance in respect of the blue LED chips. The fluorinated aromaticorganosilicon-modified polyimide is synthesized from a siloxane-typediamine, an aromatic diamine comprising a fluoro (F) group (or referredto as fluorinated aromatic diamine) and an aromatic dianhydridecomprising a fluoro (F) group (or referred to as fluorinated aromaticanhydride). In other words, both Ar¹ and Ar² comprise a fluoro (F)group. The semi-aliphatic and full aliphatic organosilicon-modifiedpolyimides are synthesized from a dianhydride, a siloxane-type diamineand at least one diamine not comprising an aromatic structure (e.g. abenzene ring) (or referred to as aliphatic diamine), or from a diamine(one of the diamine is siloxane-type diamine) and at least onedianhydride not comprising an aromatic structure (e.g. a benzene ring)(or referred to as aliphatic anhydride). In other words, at least one ofAr¹ and Ar² has an alicyclic hydrocarbon structure.

Although blue LED chips have a main light-emitting wavelength of 450 nm,they may still emit a minor light having a shorter wavelength of around400 nm, due to the difference in the conditions during the manufactureof the chips and the effect of the environment. The fluorinatedaromatic, semi-aliphatic and full aliphatic polyimides have differentabsorptions to the light having a shorter wavelength of 400 nm. Thefluorinated aromatic polyimide has an absorbance of about 20% to thelight having a shorter wavelength of around 400 nm, i.e. the lighttransmittance of the light having a wavelength of 400 nm is about 80%after passing through the fluorinated aromatic polyimide. Thesemi-aliphatic and full aliphatic polyimides have even lower absorbanceto the light having a shorter wavelength of 400 nm than the fluorinatedaromatic polyimide, which is only 12%. Accordingly, in an embodiment, ifthe LED chips used in the LED filament have a uniform quality, and emitless blue light having a shorter wavelength, the fluorinated aromaticorganosilicon-modified polyimide may be used to produce the filamentsubstrate or the light-conversion layer. In another embodiment, if theLED chips used in the LED filament have different qualities, and emitmore blue light having a shorter wavelength, the semi-aliphatic or fullaliphatic organosilicon-modified polyimides may be used to produce thefilament substrate or the light-conversion layer.

Adding different thermal curing agents imposes different effects on thelight transmittance of the organosilicon-modified polyimide. Table 1-1shows the effect of the addition of different thermal curing agents onthe light transmittance of the full aliphatic organosilicon-modifiedpolyimide. At the main light-emitting wavelength of 450 nm for the blueLED chip, the addition of different thermal curing agents renders nosignificant difference to the light transmittance of the full aliphaticorganosilicon-modified polyimide; while at a short wavelength of 380 nm,the addition of different thermal curing agents does affect the lighttransmittance of the full aliphatic organosilicon-modified polyimide.The organosilicon-modified polyimide itself has a poorer transmittanceto the light having a short wavelength (380 nm) than to the light havinga long wavelength (450 nm). However, the extent of the difference varieswith the addition of different thermal curing agents. For example, whenthe thermal curing agent KF105 is added to the full aliphaticorganosilicon-modified polyimide, the extent of the reduction in thelight transmittance is less. In comparison, when the thermal curingagent 2021p is added to the full aliphatic organosilicon-modifiedpolyimide, the extent of the reduction in the light transmittance ismore. Accordingly, in an embodiment, if the LED chips used in the LEDfilament have a uniform quality, and emit less blue light having a shortwavelength, the thermal curing agent BPA or the thermal curing agent2021p may be added. In comparison, in an embodiment, if the LED chipsused in the LED filament have different qualities, and emit more bluelight having a short wavelength, the thermal curing agent KF105 may beused. Both Table 1-1 and Table 1-2 show the results obtained in thetransmittance test using Shimadzu UV-Vis Spectrometer UV-1800. The lighttransmittances at wavelengths 380 nm, 410 nm and 450 nm are tested basedon the light emission of white LEDs.

TABLE 1-1 Thermal Light Transmittance (%) Mechanical StrengthOrganosilicon- Curing Agent Film Tensile Modified Amount 380 410 450Thickness Elongation Strength Polyimides Types (%) nm nm nm (μm) (%)(MPa) Full Aliphatic BPA 8.0 87.1 89.1 90.6 44 24.4 10.5 Full AliphaticX22-163 8.0 86.6 88.6 90.2 44 43.4 8.0 Full Aliphatic KF105 8.0 87.288.9 90.4 44 72.6 7.1 Full Aliphatic EHPE3150 8.0 87.1 88.9 90.5 44 40.913.1 Full Aliphatic 2021p 8.0 86.1 88.1 90.1 44 61.3 12.9

Even when the same thermal curing agent is added, different added amountthereof will have different effects on the light transmittance. Table1-2 shows that when the added amount of the thermal curing agent BPA tothe full aliphatic organosilicon-modified polyimide is increased from 4%to 8%, the light transmittance increases. However, when the added amountis further increased to 12%, the light transmittance keeps almostconstant. It is shown that the light transmittance increases with theincrease of the added amount of the thermal curing agent, but after thelight transmittance increases to certain degree, adding more thermalcuring agent will have limited effect on the light transmittance.

TABLE 1-2 Thermal Light Transmittance (%) Mechanical StrengthOrganosilicon- Curing Agent Film Tensile Modified Amount 380 410 450Thickness Elongation Strength Polyimide Type (%) nm nm nm (mm) (%) (MPa)Full Aliphatic BPA 4.0 86.2 88.4 89.7 44 22.5 9.8 Full Aliphatic 8.087.1 89.1 90.6 44 24.4 10.5 Full Aliphatic 12.0 87.3 88.9 90.5 44 20.19.0

TABLE 2 Organosilicon- Siloxane Thermal Tensile Elastic ElongationModified Content Curing Tg Strength Modulus at Break Chemical Resistanceto Polyimide (wt %) Agent (° C.) (MPa) (GPa) (%) TransmittanceResistance Thermochromism 1 37 BPA 158 33.2 1.7 10 85 Δ 83 2 41 BPA 14238.0 1.4 12 92 ∘ 90 3 45 BPA 145 24.2 1.1 15 97 Δ 90 4 64 BPA 30 8.90.04 232 94 ∘ 92 5 73 BPA 0 1.8 0.001 291 96 ∘ 95

Different heat dispersing particles would have different transmittances.If heat dispersing particles with low light transmittance or low lightreflection are used, the light transmittance of theorganosilicon-modified polyimide resin composition will be lower. Theheat dispersing particles in the organosilicon-modified polyimide resincomposition of the present disclosure are preferably selected to betransparent powders or particles with high light transmittance or highlight reflection. Since the soft filament for the LED is mainly for thelight emission, the filament substrate should have good lighttransmittance. In addition, when two or more types of heat dispersingparticles are mixed, particles with high light transmittance and thosewith low light transmittance can be used in combination, wherein theproportion of particles with high light transmittance is higher thanthat of particles with low light transmittance. In an embodiment, forexample, the weight ratio of particles with high light transmittance toparticles with low light transmittance is 3˜5:1.

Different siloxane content also affects the light transmittance. As canbe seen from Table 2, when the siloxane content is only 37 wt %, thelight transmittance is only 85%. When the siloxane content is increaseto above 45%, the light transmittance exceeds 94%.

Heat Resistance

The factors affecting the heat resistance of the organosilicon-modifiedpolyimide resin composition include at least the type of the mainmaterial, the siloxane content, and the type and content of the modifier(thermal curing agent).

All the organosilicon-modified polyimide resin composition synthesizedfrom fluorinated aromatic, semi-aliphatic and full aliphaticorganosilicon-modified polyimide have superior heat resistance, and aresuitable for producing the filament substrate or the light-conversionlayer. Detailed results from the accelerated heat resistance and agingtests (300° C.×1 hour) show that the fluorinated aromaticorganosilicon-modified polyimide has better heat resistance than thealiphatic organosilicon-modified polyimide. Accordingly, in anembodiment, if a high power, high brightness LED chip is used in the LEDfilament, the fluorinated aromatic organosilicon-modified polyimide maybe used to produce the filament substrate or the light-conversion layer.

The siloxane content in the organosilicon-modified polyimide will affectthe resistance to thermochromism of the organosilicon-modified polyimideresin composition. The resistance to thermochromism refers to thetransmittance determined at 460 nm after placing the sample at 200° C.for 24 hours. As can be seen from Table 2, when the siloxane content isonly 37 wt %, the light transmittance after 24 hours at 200° C. is only83%. As the siloxane content is increased, the light transmittance after24 hours at 200° C. increases gradually. When the siloxane content is 73wt %, the light transmittance after 24 hours at 200° C. is still as highas 95%. Accordingly, increasing the siloxane content can effectivelyincrease the resistance to thermochromism of the organosilicon-modifiedpolyimide.

Adding a thermal curing agent can lead to increased heat resistance andglass transition temperature. As shown in FIGS. 1, A1 and A2 representthe curves before and after adding the thermal curing agent,respectively; and the curves D1 and D2 represent the values afterdifferential computation on curves A1 and A2, respectively, representingthe extent of the change of curves A1 and A2. As can be seen from theanalysis results from TMA (thermomechanical analysis) shown in FIG. 1,the addition of the thermal curing agent leads to a trend that thethermal deformation slows down. Accordingly, adding a thermal curingagent can lead to increase of the heat resistance.

In the cross-linking reaction between the organosilicon-modifiedpolyimide and the thermal curing agent, the thermal curing agent shouldhave an organic group which is capable of reacting with the functionalgroup having active hydrogen in the polyimide. The amount and the typeof the thermal curing agent have certain effects on chromism, mechanicalproperty and refractive index of the substrate. Accordingly, a thermalcuring agent with good heat resistance and transmittance can beselected. Examples of the thermal curing agent include epoxy resin,isocyanate, bismaleimide, and bisoxazoline compounds. The epoxy resinmay be bisphenol A epoxy resin, such as BPA; or siloxane-type epoxyresin, such as KF105, X22-163, and X22-163A; or alicylic epoxy resin,such as 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexanecarboxylate(2021P), EHPE3150, and EHPE3150CE. Through the bridging reaction by theepoxy resin, a three dimensional bridge structure is formed between theorganosilicon-modified polyimide and the epoxy resin, increasing thestructural strength of the adhesive itself. In an embodiment, the amountof the thermal curing agent may be determined according to the molaramount of the thermal curing agent reacting with the functional grouphaving active hydrogen in the organosilicon-modified polyimide. In anembodiment, the molar amount of the functional group having activehydrogen reacting with the thermal curing agent is equal to that of thethermal curing agent. For example, when the molar amount of thefunctional group having active hydrogen reacting with the thermal curingagent is 1 mol, the molar amount of the thermal curing agent is 1 mol.

Thermal Conductivity

The factors affecting the thermal conductivity of theorganosilicon-modified polyimide resin composition include at least thetype and content of the fluorescent powders, the type and content of theheat dispersing particles and the addition and the type of the couplingagent. In addition, the particle size and the particle size distributionof the heat dispersing particles would also affect the thermalconductivity.

The organosilicon-modified polyimide resin composition may also comprisefluorescent powders for obtaining the desired light-emitting properties.The fluorescent powders can convert the wavelength of the light emittedfrom the light-emitting semiconductor. For example, yellow fluorescentpowders can convert blue light to yellow light, and red fluorescentpowders can convert blue light to red light. Examples of yellowfluorescent powders include transparent fluorescent powders such as(Ba,Sr,Ca)₂SiO₄:Eu, and (Sr,Ba)₂SiO₄:Eu(barium orthosilicate (BOS));silicate-type fluorescent powders having a silicate structure such asY₃Al₅O₁₂:Ce (YAG(yttrium.aluminum.garnet):Ce), and Tb₃Al₃O₁₂:Ce(YAG(terbium.aluminum.garnet):Ce); and oxynitride fluorescent powderssuch as Ca-α-SiAlON. Examples of red fluorescent powders include nitridefluorescent powders, such as CaAlSiN₃:Eu, and CaSiN₂:Eu. Examples ofgreen fluorescent powders include rare earth-halide fluorescent powders,and silicate fluorescent powders. The ratio of the fluorescent powdersin the organosilicon-modified polyimide resin composition may bedetermined arbitrarily according to the desired light-emitting property.In addition, since the fluorescent powders have a thermal conductivitywhich is significantly higher than that of the organosilicon-modifiedpolyimide resin, the thermal conductivity of the organosilicon-modifiedpolyimide resin composition as a whole will increase as the ratio of thefluorescent powders in the organosilicon-modified polyimide resincomposition increases. Accordingly, in an embodiment, as long as thelight-emitting property is fulfilled, the content of the fluorescentpowders can be suitably increased to increase the thermal conductivityof the organosilicon-modified polyimide resin composition, which isbeneficial to the heat dissipation of the filament substrate or thelight-conversion layer. Furthermore, when the organosilicon-modifiedpolyimide resin composition is used as the filament substrate, thecontent, shape and particle size of the fluorescent powders in theorganosilicon-modified polyimide resin composition also have certaineffect on the mechanical property (such as the elastic modulus,elongation, tensile strength) and the warpage extent of the substrate.In order to render superior mechanical property and thermal conductivityas well as small warpage extent to the substrate, the fluorescentpowders included in the organosilicon-modified polyimide resincomposition are particulate, and the shape thereof may be sphere, plateor needle, preferably sphere. The maximum average length of thefluorescent powders (the average particle size when they are spherical)is above 0.1 preferably over 1 further preferably 1˜100 and morepreferably 1˜50 The content of fluorescent powders is no less than 0.05times, preferably no less than 0.1 times, and no more than 8 times,preferably no more than 7 times, the weight of theorganosilicon-modified polyimide. For example, when the weight of theorganosilicon-modified polyimide is 100 parts in weight, the content ofthe fluorescent powders is no less than 5 parts in weight, preferably noless than 10 parts in weight, and no more than 800 parts in weight,preferably no more than 700 parts in weight. When the content of thefluorescent powders in the organosilicon-modified polyimide resincomposition exceeds 800 parts in weight, the mechanical property of theorganosilicon-modified polyimide resin composition may not achieve thestrength as required for a filament substrate, resulting in the increaseof the defective rate of the product. In an embodiment, two kinds offluorescent powders are added at the same time. For example, when redfluorescent powders and green fluorescent powders are added at the sametime, the added ratio of red fluorescent powders to green fluorescentpowders is 1:5˜8, preferably 1:6˜7. In another embodiment, redfluorescent powders and yellow fluorescent powders are added at the sametime, wherein the added ratio of red fluorescent powders to yellowfluorescent powders is 1:5˜8, preferably 1:6˜7. In another embodiment,three or more kinds of fluorescent powders are added at the same time.

The main purposes of adding the heat dispersing particles are toincrease the thermal conductivity of the organosilicon-modifiedpolyimide resin composition, to maintain the color temperature of thelight emission of the LED chip, and to prolong the service life of theLED chip. Examples of the heat dispersing particles include silica,alumina, magnesia, magnesium carbonate, aluminum nitride, boron nitrideand diamond. Considering the dispersity, silica, alumina or combinationthereof is preferably. The shape of the heat dispersing particles may besphere, block, etc., where the sphere shape encompasses shapes which aresimilar to sphere. In an embodiment, heat dispersing particles may be ina shape of sphere or non-sphere, to ensure the dispersity of the heatdispersing particles and the thermal conductivity of the substrate,wherein the added weight ratio of the spherical and non-spherical heatdispersing particles is 1:0.15˜0.35.

TABLE 3-1 Weight Ratio [wt %] 0.0% 37.9% 59.8% 69.8% 77.6% 83.9% 89.0%Volume Ratio [vol %] 0.0% 15.0% 30.0% 40.0% 50.0% 60.0% 70.0% ThermalConductivity[W/m*K] 0.17 0.20 0.38 0.54 0.61 0.74 0.81

Table 3-1 shows the relationship between the content of the heatdispersing particles and the thermal conductivity of theorganosilicon-modified polyimide resin composition. As the content ofthe heat dispersing particles increases, the thermal conductivity of theorganosilicon-modified polyimide resin composition increases. However,when the content of the heat dispersing particles in theorganosilicon-modified polyimide resin composition exceeds 1200 parts inweight, the mechanical property of the organosilicon-modified polyimideresin composition may not achieve the strength as required for afilament substrate, resulting in the increase of the defective rate ofthe product. In an embodiment, high content of heat dispersing particleswith high light transmittance or high reflectivity (such as SiO₂, Al₂O₃)may be added, which, in addition to maintaining the transmittance of theorganosilicon-modified polyimide resin composition, increases the heatdissipation of the organosilicon-modified polyimide resin composition.The heat conductivities shown in Tables 3-1 and 3-2 were measured by athermal conductivity meter DRL-III manufactured by Xiangtan cityinstruments Co., Ltd. under the following test conditions: heatingtemperature: 90° C.; cooling temperature: 20° C.; load: 350N, aftercutting the resultant organosilicon-modified polyimide resin compositioninto test pieces having a film thickness of 300 μm and a diameter of 30mm.

For the effects of the particle size and the particle size distributionof the heat dispersing particles on the thermal conductivity of theorganosilicon-modified polyimide resin composition, see both Table 3-2and FIG. 2. Table 3-2 and FIG. 2 show 7 heat dispersing particles withdifferent specifications added into the organosilicon-modified polyimideresin composition in the same ratio and their effects on the thermalconductivity. The particle size of the heat dispersing particlessuitable to be added to the organosilicon-modified polyimide resincomposition can be roughly classified as small particle size (less than1 μm), medium particle size (1-30 μm) and large particle size (above 30μm).

Comparing specifications 1, 2 and 3, wherein only heat dispersingparticles with medium particle size but different average particle sizesare added, when only heat dispersing particles with medium particle sizeare added, the average particle size of the heat dispersing particlesdoes not significantly affect the thermal conductivity of theorganosilicon-modified polyimide resin composition. Comparingspecifications 3 and 4, wherein the average particle sizes are similar,the specification 4 comprising small particle size and medium particlesize obviously exhibits higher thermal conductivity than specification 3comprising only medium particle size. Comparing specifications 4 and 6,which comprise heat dispersing particles with both small particle sizeand medium particle size, although the average particle sizes of theheat dispersing particles are different, they have no significant effecton the thermal conductivity of the organosilicon-modified polyimideresin composition. Comparing specifications 4 and 7, specification 7,which comprises heat dispersing particles with large particle size inaddition to small particle size and medium particle size, exhibits themost excellent thermal conductivity. Comparing specifications 5 and 7,which both comprise heat dispersing particles with large, medium andsmall particle sizes and have similar average particle sizes, thethermal conductivity of specification 7 is significant superior to thatof specification 5 due to the difference in the particle sizedistribution. See FIG. 2 for the particle size distribution ofspecification 7, the curve is smooth, and the difference in the slope issmall, showing that specification 7 not only comprises each particlesize, but also have moderate proportions of each particle size, and theparticle size is normally distributed. For example, the small particlesize represents about 10%, the medium particle size represents about60%, and the large particle size represents about 30%. In contrast, thecurve for specification 5 has two regions with large slopes, whichlocate in the regions of particle size 1-2 μm and particle size 30-70respectively, indicating that most of the particle size in specification5 is distributed in particle size 1-2 μm and particle size 30-70 andonly small amount of heat dispersing particles with particle size 3-20μm are present, i.e. exhibiting a two-sided distribution.

TABLE 3-2 Specification 1 2 3 4 5 6 7 Average Particle Size [μm] 2.7 6.6  9.0  9.6  13    4.1  12    Particle Size Distribution [μm] 1~7 1~201~30 0.2~30 0.2~110 0.1~20 0.1~100 Thermal Conductivity [W/m*K] 1.651.48 1.52 1.86 1.68 1.87 2.10

Accordingly, the extent of the particle size distribution of the heatdispersing particles affecting the thermal conductivity is greater thanthat of the average particle size of the heat dispersing particles. Whenlarge, medium and small particle sizes of the heat dispersing particlesare added, and the small particle size represents about 5-20%, themedium particle size represents about 50-70%, and large particle sizerepresents about 20-40%, the organosilicon-modified polyimide resin willhave optimum thermal conductivity. That is because when large, mediumand small particle sizes are present, there would be denser packing andcontacting each other of heat dispersing particles in a same volume, soas to form an effective heat dissipating route.

In an embodiment, for example, alumina with a particle size distributionof 0.1˜100 μm and an average particle size of 12 μm or with a particlesize distribution of 0.1˜20 μm and an average particle size of 4.1 μm isused, wherein the particle size distribution is the range of theparticle size of alumina. In another embodiment, considering thesmoothness of the substrate, the average particle size may be selectedas ⅕˜⅖, preferably ⅕˜⅓ of the thickness of the substrate. The amount ofthe heat dispersing particles may be 1˜12 times the weight (amount) ofthe organosilicon-modified polyimide. For example, if the amount of theorganosilicon-modified polyimide is 100 parts in weight, the amount ofthe heat dispersing particles may be 100˜1200 parts in weight,preferably 400˜900 parts in weight. Two different heat dispersingparticles such as silica and alumina may be added at the same time,wherein the weight ratio of alumina to silica may be 0.4˜25:1,preferably 1˜10:1.

In the synthesis of the organosilicon-modified polyimide resincomposition, a coupling agent such as a silicone coupling agent may beadded to improve the adhesion between the solid material (such as thefluorescent powders and/or the heat dispersing particles) and theadhesive material (such as the organosilicon-modified polyimide), and toimprove the dispersion uniformity of the whole solid materials, and tofurther improve the heat dissipation and the mechanical strength of thelight-conversion layer. The coupling agent may also be titanate couplingagent, preferably epoxy titanate coupling agent. The amount of thecoupling agent is related to the amount of the heat dispersing particlesand the specific surface area thereof. The amount of the couplingagent=(the amount of the heat dispersing particles*the specific surfacearea of the heat dispersing particles)/the minimum coating area of thecoupling agent. For example, when an epoxy titanate coupling agent isused, the amount of the coupling agent=(the amount of the heatdispersing particles*the specific surface area of the heat dispersingparticles)/331.5.

In other specific embodiments of the present disclosure, in order tofurther improve the properties of the organosilicon-modified polyimideresin composition in the synthesis process, an additive such as adefoaming agent, a leveling agent or an adhesive may be selectivelyadded in the process of synthesizing the organosilicon-modifiedpolyimide resin composition, as long as it does not affect lightresistance, mechanical strength, heat resistance and chromism of theproduct. The defoaming agent is used to eliminate the foams produced inprinting, coating and curing. For example, acrylic acid or siliconesurfactants may be used as the defoaming agent. The leveling agent isused to eliminate the bumps in the film surface produced in printing andcoating. Specifically, adding preferably 0.01˜2 wt % of a surfactantcomponent can inhibit foams. The coating film can be smoothened by usingacrylic acid or silicone leveling agents, preferably non-ionicsurfactants free of ionic impurities. Examples of the adhesive includeimidazole compounds, thiazole compounds, triazole compounds,organoaluminum compounds, organotitanium compounds and silane couplingagents. Preferably, the amount of these additives is no more than 10% ofthe weight of the organosilicon-modified polyimide. When the mixedamount of the additive exceeds 10 wt %, the physical properties of theresultant coating film tend to decline, and it even leads todeterioration of the light resistance due to the presence of thevolatile components.

Mechanical Strength

The factors affecting the mechanical strength of theorganosilicon-modified polyimide resin composition include at least thetype of the main material, the siloxane content, the type of themodifier (thermal curing agent), the fluorescent powders and the contentof the heat dispersing particles.

Different organosilicon-modified polyimide resins have differentproperties. Table 4 lists the main properties of the fluorinatedaromatic, semi-aliphatic and full aliphatic organosilicon-modifiedpolyimide, respectively, with a siloxane content of about 45% (wt %).The fluorinated aromatic has the best resistance to thermochromism. Thefull aliphatic has the best light transmittance. The fluorinatedaromatic has both high tensile strength and high elastic modulus. Theconditions for testing the mechanical strengths shown in Table 4˜6: theorganosilicon-modified polyimide resin composition has a thickness of 50μm and a width of 10 mm, and the tensile strength of the film isdetermined according to ISO527-3:1995 standard with a drawing speed of10 mm/min.

TABLE 4 Organosilicon- Siloxane Thermal Tensile Elastic ElongationModified Content Curing Strength Modulus at Break Resistance toPolyimide (wt %) Agent (MPa) (GPa) (%) Transmittance ThermochromismFluorinated 44 X22-163 22.4 1.0 83 96 95 Aromatic Semi-Aliphatic 44X22-163 20.4 0.9 30 96 91 Full Aliphatic 47 X22-163 19.8 0.8 14 98 88

In the manufacture of the filament, the LED chip and the electrodes arefirst fixed on the filament substrate formed by theorganosilicon-modified polyimide resin composition with a die bondingglue, followed by a wiring procedure, in which electric connections areestablished between adjacent LED chips and between the LED chip and theelectrode with wires. To ensure the quality of die bonding and wiring,and to improve the product quality, the filament substrate should have acertain level of elastic modulus to resist the pressing force in the diebonding and wiring processes. Accordingly, the filament substrate shouldhave an elastic modulus more than 2.0 GPa, preferably 2˜6 GPa, morepreferably 4˜6 GPa. Table 5 shows the effects of different siloxanecontents and the presence of particles (fluorescent powders and alumina)on the elastic modulus of the organosilicon-modified polyimide resincomposition. Where no fluorescent powder or alumina particle is added,the elastic modulus of the organosilicon-modified polyimide resincomposition is always less than 2.0 GPa, and as the siloxane contentincreases, the elastic modulus tends to decline, i.e. theorganosilicon-modified polyimide resin composition tends to soften.However, where fluorescent powders and alumina particles are added, theelastic modulus of the organosilicon-modified polyimide resincomposition may be significantly increased, and is always higher than2.0 GPa. Accordingly, the increase in the siloxane content may lead tosoftening of the organosilicon-modified polyimide resin composition,which is advantageous for adding more fillers, such as more fluorescentpowders or heat dispersing particles. In order for the substrate to havesuperior elastic modulus and thermal conductivity, appropriate particlesize distribution and mixing ratio may be selected so that the averageparticle size is within the range from 0.1 μm to 100 μm or from 1 μm to50 μm.

In order for the LED filament to have good bending properties, thefilament substrate should have an elongation at break of more than 0.5%,preferably 1˜5%, most preferably 1.5˜5%. As shown in Table 5, where nofluorescent powder or alumina particle is added, theorganosilicon-modified polyimide resin composition has excellentelongation at break, and as the siloxane content increases, theelongation at break increases and the elastic modulus decreases, therebyreducing the occurrence of warpage. In contrast, where fluorescentpowders and alumina particles are added, the organosilicon-modifiedpolyimide resin composition exhibits decreased elongation at break andincreased elastic modulus, thereby increasing the occurrence of warpage.

TABLE 5 Addition of Siloxane Fluorescent Thermal Tensile ElasticElongation Content Powders, Curing Tg Strength Modulus at Break ChemicalResistance to (wt %) Alumina Agent (° C.) (MPa) (GPa) (%) TransmittanceResistance Thermochromism 37 x BPA 158 33.2 1.7 10 85 Δ 83 37 ∘ BPA —26.3 5.1 0.7 — — — 41 x BPA 142 38.0 1.4 12 92 ∘ 90 41 ∘ BPA — 19.8 4.80.8 — — — 45 x BPA 145 24.2 1.1 15 97 Δ 90 45 ∘ BPA — 21.5 4.2 0.9 — — —64 x BPA  30 8.9 0.04 232 94 ∘ 92 64 ∘ BPA — 12.3 3.1 1.6 — — — 73 x BPA 0 1.8 0.001 291 96 ∘ 95 73 ∘ BPA — 9.6 2.5 2 — — —

By adding a thermal curing agent, not only the heat resistance and theglass transition temperature of the organosilicon-modified polyimideresin are increased, the mechanical properties, such as tensilestrength, elastic modulus and elongation at break, of theorganosilicon-modified polyimide are also increased. Adding differentthermal curing agents may lead to different levels of improvement. Table6 shows the tensile strength and the elongation at break of theorganosilicon-modified polyimide resin composition after the addition ofdifferent thermal curing agents. For the full aliphaticorganosilicon-modified polyimide, the addition of the thermal curingagent EHPE3150 leads to good tensile strength, while the addition of thethermal curing agent KF105 leads to good elongation.

TABLE 6 Thermal Transmittance (%) Mechanical Strength Organosilicon-Curing Agent Film Tensile Modified Amount 380 410 450 ThicknessElongation Strength Polyimide Type (%) nm nm nm (μm) (%) (MPa) FullAliphatic BPA 8.0 87.1 89.1 90.6 44 24.4 10.5 Full Aliphatic X22-163 8.086.6 88.6 90.2 40 43.4 8.0 Full Aliphatic KF105 12.0 87.5 89.2 90.8 4380.8 7.5 Full Aliphatic EHPE3150 7.5 87.1 88.9 90.5 44 40.9 13.1 FullAliphatic 2021p 5.5 86.1 88.1 90.1 44 64.0 12.5

TABLE 7 Specific Information of BPA Content of Viscosity HydrolysableEquivalent Product at 25° C. Color Chlorine of Epoxy Hue Name (mPa · s)(G) (mg/kg) (g/mol) APHA BPA 11000-15000 ≤1 ≤300 184-194 ≤30

TABLE 8 Specific Information of2021P Viscosity Specific Melting BoilingWater Equivalent Product at 25° C. Gravity Point Point Content of EpoxyHue Name (mPa · s) (25/25° C.) (° C.) (° C./4 hPa) (%) (g/mol) APHA2021P 250 1.17 −20 188 0.01 130 10

TABLE 9 Specific Information ofEHPE3150 andEHPE3150CE ViscosityEquivalent Product at 25° C. Softening of Epoxy Hue Name (mPa · s)Appearance Point (g/mol) APHA EHPE3150 — Transparent 75 177 20 (in 25%Plate Solid acetone solution) EHPE3150CE 50,000 Light Yellow — 151 60Transparent Liquid

TABLE 10 Specific Information of PAME, KF8010, X22-161A, X22-161B,NH15D, X22-163, X22-163A andKF-105 Viscosity Specific Refractive Productat 25° C. Gravity Index Equivalent of Name (mm²/s) at 25° C. at 25° C.Functional Group PAME 4 0.90 1.448 130 g/mol KF8010 12 1.00 1.418 430g/mol X22-161A 25 0.97 1.411 800 g/mol X22-161B 55 0.97 1.408 1500 g/molNH15D 13 0.95 1.403 1.6~2.1 g/mmol X22-163 15 1.00 1.450 200 g/molX22-163A 30 0.98 1.413 1000 g/mol KF-105 15 0.99 1.422 490 g/mol

The organosilicon-modified polyimide resin composition of the presentdisclosure may be used in a form of film or as a substrate together witha support to which it adheres. The film forming process comprises threesteps: (a) coating step: spreading the above organosilicon-modifiedpolyimide resin composition on a peelable body by coating to form afilm; (b) heating and drying step: heating and drying the film togetherwith the peelable body to remove the solvent from the film; and (c)peeling step: peeling the film from the peelable body after the dryingis completed to give the organosilicon-modified polyimide resincomposition in a form of film. The above peelable body may be acentrifugal film or other materials which do not undergo chemicalreaction with the organosilicon-modified polyimide resin composition,e.g., PET centrifugal film.

The organosilicon-modified polyimide resin composition may be adhered toa support to give an assembly film, which may be used as the substrate.The process of forming the assembly film comprises two steps: (a)coating step: spreading the above organosilicon-modified polyimide resincomposition on a support by coating to from an assembly film; and (b)heating and drying step: heating and drying the assembly film to removethe solvent from the film.

In the coating step, roll-to-roll coating devices such as roller coater,mold coating machine and blade coating machine, or simple coating meanssuch as printing, inkjeting, dispensing and spraying may be used.

The drying method in the above heating and drying step may be drying invacuum, drying by heating, or the like. The heating may be achieved by aheat source such as an electric heater or a heating media to produceheat energy and indirect convection, or by infrared heat radiationemitted from a heat source.

A film (composite film) with high thermal conductivity can be obtainedfrom the above organosilicon-modified polyimide resin composition bycoating and then drying and curing, so as to achieve any one orcombination of the following properties: superior light transmittance,chemical resistance, heat resistance, thermal conductivity, filmmechanical property and light resistance. The temperature and time inthe drying and curing step may be suitably selected according to thesolvent and the coated film thickness of the organosilicon-modifiedpolyimide resin composition. The weight change of theorganosilicon-modified polyimide resin composition before and after thedrying and curing as well as the change in the peaks in the IR spectrumrepresenting the functional groups in the thermal curing agent can beused to determine whether the drying and curing are completed. Forexample, when an epoxy resin is used as the thermal curing agent,whether the difference in the weight of the organosilicon-modifiedpolyimide resin composition before and after the drying and curing isequal to the weight of the added solvent as well as the increase ordecrease of the epoxy peak before and after the drying and curing areused to determine whether the drying and curing are completed.

In an embodiment, the amidation is carried out in a nitrogen atmosphere,or vacuum defoaming is employed in the synthesis of theorganosilicon-modified polyimide resin composition, or both, so that thevolume percentage of the cells in the organosilicon-modified polyimideresin composition composite film is 5˜20%, preferably 5˜10%. As shown inFIG. 4a , the organosilicon-modified polyimide resin compositioncomposite film is used as the substrate for the LED soft filament. Thesubstrate 420 b has an upper surface 420 b 1 and an opposite lowersurface 420 b 2. FIG. 3 shows the surface morphology of the substrateafter gold is scattered on the surface thereof as observed with vega3electron microscope from Tescan Corporation. As can be seen from FIG. 4aand the SEM image of the substrate surface shown in FIG. 3, there is acell 4d in the substrate, wherein the cell 4d represents 5˜20% byvolume, preferably 5˜10% by volume, of the substrate 420 b, and thecross section of the cell 4d is irregular. FIG. 4a shows thecross-sectional scheme of the substrate 420 b, wherein the dotted lineis the baseline. The upper surface 420 b 1 of the substrate comprises afirst area 4 a and a second area 4 b, wherein the second area 4 bcomprises a cell 4d, and the first area 4 a has a surface roughnesswhich is less than that of the second area 4 b. The light emitted by theLED chip passes through the cell in the second area and is scattered, sothat the light emission is more uniform. The lower surface 420 b 2 ofthe substrate comprises a third area 4 c, which has a surface roughnesswhich is higher than that of the first area 4 a. When the LED chip ispositioned in the first area 4 a, the smoothness of the first area 4 ais favorable for subsequent bonding and wiring. When the LED chip ispositioned in the second area 4 b or the third area 4 c, the area ofcontact between the die bonding glue and substrate is large, whichimproves the bonding strength between the die bonding glue andsubstrate. Therefore, by positioning the LED chip on the upper surface420 b 1, bonding and wiring as well as the bonding strength between thedie bonding glue and substrate can be ensured at the same time. When theorganosilicon-modified polyimide resin composition is used as thesubstrate of the LED soft filament, the light emitted by the LED chip isscattered by the cell in the substrate, so that the light emission ismore uniform, and glare can be further improved at the same time. In anembodiment, the surface of the substrate 420 b may be treated with asilicone resin or a titanate coupling agent, preferably a silicone resincomprising methanol or a titanate coupling agent comprising methanol, ora silicone resin comprising isopropanol. The cross section of thetreated substrate is shown in FIG. 4b . The upper surface 420 b 1 of thesubstrate has relatively uniform surface roughness. The lower surface420 b 2 of the substrate comprises a third area 4 c and a fourth area 4e, wherein the third area 4 c has a surface roughness which is higherthan that of the fourth area 4 e. The surface roughness of the uppersurface 420 b 1 of the substrate may be equal to that of the fourth area4 e. The surface of the substrate 420 b may be treated so that amaterial with a high reactivity and a high strength can partially enterthe cell 4d, so as to improve the strength of the substrate.

When the organosilicon-modified polyimide resin composition is preparedby vacuum defoaming, the vacuum used in the vacuum defoaming may be−0.5˜−0.09 MPa, preferably −0.2˜0.09 MPa. When the total weight of theraw materials used in the preparation of the organosilicon-modifiedpolyimide resin composition is less than or equal to 250 g, therevolution speed is 1200˜2000 rpm, the rotation speed is 1200˜2000 rpm,and time for vacuum defoaming is 3˜8 min. This not only maintainscertain amount of cells in the film to improve the uniformity of lightemission, but also keeps good mechanical properties. The vacuum may besuitably adjusted according to the total weight of the raw materialsused in the preparation of the organosilicon-modified polyimide resincomposition. Normally, when the total weight is higher, the vacuum maybe reduced, while the stirring time and the stirring speed may besuitably increased.

According to the present disclosure, a resin having superiortransmittance, chemical resistance, resistance to thermochromism,thermal conductivity, film mechanical property and light resistance asrequired for a LED soft filament substrate can be obtained. In addition,a resin film having a high thermal conductivity can be formed by simplecoating methods such as printing, inkjeting, and dispensing.

When the organosilicon-modified polyimide resin composition compositefilm is used as the filament substrate (or base layer), the LED chip isa hexahedral luminous body. In the production of the LED filament, atleast two sides of the LED chip are coated by a top layer. When theprior art LED filament is lit up, non-uniform color temperatures in thetop layer and the base layer would occur, or the base layer would give agranular sense. Accordingly, as a filament substrate, the composite filmis required to have superior transparency. In other embodiments,sulfonyl group, non-coplanar structure, meta-substituted diamine, or thelike may be introduced into the backbone of the organosilicon-modifiedpolyimide to improve the transparency of the organosilicon-modifiedpolyimide resin composition. In addition, in order for the bulbemploying said filament to achieve omnidirectional illumination, thecomposite film as the substrate should have certain flexibility.Therefore, flexible structures such as ether (such as(4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl ether), carbonyl,methylene may be introduced into the backbone of theorganosilicon-modified polyimide. In other embodiments, a diamine ordianhydride comprising a pyridine ring may be employed, in which therigid structure of the pyridine ring can improve the mechanicalproperties of the composite film. Meanwhile, by using it together with astrong polar group such as —F, the composite film may have superiorlight transmittance. Examples of the anhydride comprising a pyridinering include2,6-bis(3′,4′-dicarboxyphenyl)-4-(3″,5″-bistrifluoromethylphenyl)pyridinedianhydride.

As shown in FIG. 5, the LED filament 100 comprises a plurality of LEDchips 102, 104; at least two electrodes 110, 112; and alight-conversionlayer 120 comprising an adhesive 122 and wavelength conversion particles124. The adhesive 122 may be the above organosilicon-modified polyimide,so as to have better toughness, and reduce the occurrence of cracking orbrittleness. The light conversion particles in the light-conversionlayer 120 (which may be any light conversion material such asfluorescent powders or dye, and fluorescent powders 124 are describedhereinafter as an example) can absorb certain radiation (e.g., light) toemit light. The light-conversion layer 120 may further compriseinorganic heat dispersing particles to improve the heat dissipationability.

As shown in FIG. 6, the LED filament 400 a comprises a light-conversionlayer 420; LED chips 402, 404; electrodes 410, 412; and gold wires 440for electrically connecting an LED chip to another LED chip (or to anelectrode). The light-conversion layer 420 is coated on at least twosides of the LED chip/electrode. The light-conversion layer 420 exposesa portion of the electrodes 410, 412. The light-conversion layer 420 maycomprise at least a top layer 420 a and a base layer 420 b, as the toplayer and the base layer of the filament, respectively. In thisembodiment, the top layer 420 a and the base layer 420 b are located attwo sides of the LED chip/electrode, respectively.

The top layer 420 a has a layered structure of at least one layer. Thelayered structure may be selected from a fluorescent powder adhesivelayer having a high plasticity, a fluorescent powder film layer having alow plasticity, a transparent layer or any layered combination thereof.Each of the fluorescent powder adhesive layer and the fluorescent powderfilm layer of the top layer 420 a can comprise an adhesive 422,fluorescent powders 424, and inorganic oxide nanoparticles 426. Theadhesive 422 may be, but not limited to, silica gel. In an embodiment,the adhesive 422 may comprise 10 wt % or less the aboveorganosilicon-modified polyimide, to improve the overall hardness,insulation, thermal stability and mechanical strength of the filament.The solid content of the organosilicon-modified polyimide may be 5-40 wt%, and the rotational viscosity may be 5-20 Pa. S. The inorganic oxidenanoparticles 426 may be, but not limited to, alumina and aluminumnitride particles, and the particle size thereof may be 100-600 nm or0.1-100 μm. Its function is to improve the heat dissipation of thefilament. The incorporated inorganic heat dispersing particles may havevariousparticle sizes. Suitable adjustment may be made to differentiatethe particles as required in their properties such as hardness (e.g., byadjusting the composition of the packaging adhesive or the ratio of thefluorescent powders), conversion of wavelength, particle size of thecomponents, thickness and transmittance. The percent of transmittance ofthe fluorescent powder adhesive layer or the fluorescent powder filmlayer of the top layer 420 a can be varied depending on needs. Forexample, the percent of transmittance of the fluorescent powder adhesivelayer or the fluorescent powder film layer of the top layer 420 a can begreater than 20%, 50%; or 70%. The fluorescent powder adhesive may havea Shore D hardness of 40-70 and a thickness of 0.2-1.5 mm; while thefluorescent powder film may have a Shore D hardness of 20-70, athickness of 0.1-0.5 mm, a refractive index of 1.4 or above, and atransmittance of 40%-95%. The transparent layer (adhesive layer,insulating layer) may be composed of a high tranmittance resin such assilica gel, the above organosilicon-modified polyimide, or a combinationthereof. In an embodiment, the transparent layer may be used as arefractive index matching layer, playing a role of adjusting the lightemission efficiency of the filament.

The base layer has a layered structure of at least one layer. Thelayered structure may be selected from a fluorescent powder adhesivelayer having a high plasticity, a fluorescent powder film layer having alow plasticity, a transparent layer or any layered combination thereof.Each of the fluorescent powder adhesive layer and the fluorescent powderfilm layer of the top layer 420 a can comprise organosilicon-modifiedpolyimide 422′, fluorescent powders 424′, and inorganic oxidenanoparticles 426′. In an embodiment, the organosilicon-modifiedpolyimide may be replaced by the above organosilicon-modified polyimideresin composition. The inorganic oxide nanoparticles 426 may be, but notlimited to, alumina and aluminum nitride particles, and the particlesize thereof may be 100-600 nm or 0.1-100 μm. Its function is to improvethe heat dissipation of the filament. The incorporated inorganic heatdispersing particles may have various particle sizes. The percent oftransmittance of the fluorescent powder adhesive layer or thefluorescent powder film layer of the base layer 420 b can be varieddepending on needs. For example, the percent of transmittance of thefluorescent powder adhesive layer or the fluorescent powder film layerof the base layer 420 b can be greater than 20%, 50%; or 70%. Thetransparent layer (adhesive layer, insulating layer) may be composed ofa high tranmittance resin such as silica gel, the aboveorganosilicon-modified polyimide, or a combination thereof. In anembodiment, the transparent layer may be used as a refractive indexmatching layer, playing a role of adjusting the light emissionefficiency of the filament. In an embodiment, the base layer may be theabove organosilicon-modified polyimide resin composition composite film.

As shown in FIG. 7, the LED bulb 10 c comprises a lamp shell 12, a lampholder 16 connected to the lamp shell 12, at least two conductivesupports 14 a, 14 b disposed within the lamp shell 12, a driving circuit18, cantilevers 15, a stem 19, and one LED filament 100. The conductivesupports 14 a, 14 b are used to electrically connecting two electrodes110, 112 of the LED filament, or to support the weight of the LEDfilament 100. The LED filament 100 is connected to the stem 19 throughthe conductive supports 14 a, 14 b, and the stem 19 may be used to drawthe gas in the LED bulb 10 b and to provide thermal conductivity. Thestem 19 further has a stand 19 a which vertically extends to the centerof the lamp shell 12. Each cantilever 15 has a first end which isconnected to the stand 19 a, and a second end which is connected to theLED filament. The driving circuit 18 electrically connects theconductive supports 14 a, 14 b to the lamp holder 16. When the lampholder 16 is connected to a conventional lamp socket, the lamp socketprovides power for the lamp holder 16, and the driving circuit 18obtains power from the lamp holder 16 and drives the LED filament 100 toemit light. Since the LED filament 100 can provide omnidirectionalillumination, the whole LED bulb can provide omnidirectionalillumination. The LED filament 100 may be any LED filament shown inFIGS. 4-5.

The definition of the term “omnidirectional illumination” herein dependson the specifications in various countries for specific bulbs, and mayvary with time. Accordingly, the examples provided herein ofomnidirectional illumination is not intended to limit the scope of thepresent disclosure. For the definition of the omnidirectionalillumination, reference may be made to, for example, US Energy StarProgram Requirements for Lamps (Light Bulbs), which provides adefinition of the light patternof the light bulb (omnidirectional lamp):when the bulb is disposed in a direction that the base is up and thebulb is down, the upward direction is set as 180°, and the downwarddirection is set as 0°, the requirements are: the difference between theluminous intensity (cd) at any angle in the range of 0-135° and theaverage luminous intensity should not exceed 25%, while the total flux(lm) in the range of 135-180° represents at least 5% of the whole bulb.As another example, JEL 801 Specification of Japan requires that for LEDlamps, the flux in the range of 120° should be less than 70% of thetotal flux.

The present disclosure is disclosed above by referring to optimumembodiments. However, it should be understood by a person skilled in theart that these embodiments are only used to describe some ways ofimplementing the present disclosure, and should not be construed asbeing restrictive. It should be noted that any change or modificationequivalent to these embodiments and any reasonable combinations of theseembodiments should all be within the scope being supported by thedescription. Therefore, the scope of the present disclosure should bedetermined by the appended claims.

What is claimed is:
 1. An organosilicon-modified polyimide resincomposition, comprising an organosilicon-modified polyimide and athermal curing agent, wherein the organosilicon-modified polyimidecomprises a repeating unit represented by the following general formula(I):

wherein Ar¹ is a tetra-valent organic group having a benzene ring or analicyclic hydrocarbon structure, Ar² is a di-valent organic group havinga monocyclic alicyclic hydrocarbon structure, R is each independentlymethyl or phenyl, n is 1˜5, and wherein the organosilicon-modifiedpolyimide has a number average molecular weight of 5000˜100000, andwherein the thermal curing agent is selected from the group consistingof epoxy resin, isocyanate and bisoxazoline compounds.
 2. Theorganosilicon-modified polyimide resin composition according to claim 1,wherein the organosilicon-modified polyimide has a number averagemolecular weight of 10000˜60000.
 3. The organosilicon-modified polyimideresin composition according to claim 1, wherein theorganosilicon-modified polyimide has a number average molecular weightof 20000˜40000.
 4. The organosilicon-modified polyimide resincomposition according to claim 1, wherein Ar¹ is a tetra-valent organicgroup having a monocyclic alicyclic hydrocarbon structure or abridged-ring alicyclic hydrocarbon structure.
 5. Theorganosilicon-modified polyimide resin composition according to claim 1,wherein Ar¹ is a tetra-valent organic group having a benzene ring or analicyclic hydrocarbon structure comprising a functional group havingactive hydrogen, wherein the functional group having active hydrogen isany one of hydroxyl, amino, carboxy and mercapto.
 6. Theorganosilicon-modified polyimide resin composition according to claim 1,wherein Ar² is a di-valent organic group comprising a functional grouphaving active hydrogen, wherein the functional group having activehydrogen is any one of hydroxyl, amino, carboxy and mercapto.
 7. Theorganosilicon-modified polyimide resin composition according to claim 1,wherein Ar¹ is derived from a dianhydride, and Ar² is derived from adiamine.
 8. The organosilicon-modified polyimide resin compositionaccording to claim 7, wherein 5˜25% by molar of the total amount ofdiamine comprises a functional group having active hydrogen.
 9. Theorganosilicon-modified polyimide resin composition according to claim 1,wherein siloxane content in the organosilicon-modified polyimide is20˜75 wt %.
 10. The organosilicon-modified polyimide resin compositionaccording to claim 1, wherein siloxane content in theorganosilicon-modified polyimide is 30˜70 wt %, and the composition hasa glass transition temperature of below 150° C.
 11. Theorganosilicon-modified polyimide resin composition according to claim 5,wherein the molar ratio of the thermal curing agent to the functionalgroup having active hydrogen in the organosilicon-modified polyimide is1:1.
 12. The organosilicon-modified polyimide resin compositionaccording to claim 6, wherein the molar ratio of the thermal curingagent to the functional group having active hydrogen in theorganosilicon-modified polyimide is 1:1.
 13. The organosilicon-modifiedpolyimide resin composition according to claim 1, wherein thecomposition further comprises an additive which is selected from thegroup consisting of fluorescent powders, heat dispersing particles and acoupling agent.
 14. The organosilicon-modified polyimide resincomposition according to claim 13, wherein the weight of the heatdispersing particles is 1˜12 times the weight of theorganosilicon-modified polyimide.
 15. The organosilicon-modifiedpolyimide resin composition according to claim 13, wherein the heatdispersing particles are one or more selected from the group consistingof silica, alumina, magnesium oxide, magnesium carbonate, aluminumnitride, boron nitride and diamond.
 16. The organosilicon-modifiedpolyimide resin composition according to claim 13, wherein the heatdispersing particles have a particle size distribution of 0.1˜100 μm.17. The organosilicon-modified polyimide resin composition according toclaim 13, wherein the heat dispersing particles have a particle sizedistribution from 1 μm to 50 μm.
 18. The organosilicon-modifiedpolyimide resin composition according to claim 13, wherein the heatdispersing particles have a particle size distribution of 0.1˜100 μm,and the content of small particle size of below 1 μm is 5-20%, thecontent of medium particle size of 1-30 μm is 50-70%, and the content oflarge particle size of above 30 μm is 20-40%.
 19. Theorganosilicon-modified polyimide resin composition according to claim13, wherein the fluorescent powders have an average particle size ofabove 0.1 μm.
 20. The organosilicon-modified polyimide resin compositionaccording to claim 13, wherein the fluorescent powders have an averageparticle size from 1 μm to 100 μm.
 21. The organosilicon-modifiedpolyimide resin composition according to claim 13, wherein thefluorescent powders have an average particle size from 1 to 50 μm. 22.The organosilicon-modified polyimide resin composition according toclaim 13, wherein the weight ratio of the fluorescent powders to theorganosilicon-modified polyimide is 50˜800:100.
 23. Theorganosilicon-modified polyimide resin composition according to claim13, wherein the weight ratio of the fluorescent powders to theorganosilicon-modified polyimide is 100˜700:100.
 24. Theorganosilicon-modified polyimide resin composition according to claim 1,wherein the composition further comprises one or more of a defoamingagent, a leveling agent and an adhesive.
 25. A filament substrate, whichis formed from the organosilicon-modified polyimide resin compositionaccording to claim
 1. 26. The filament substrate according to claim 25,having at least one of the following properties: a thermal conductivityof more than 1.8 W/m*K; an elastic modulus of more than 2.0 GPa; and anelongation at break of more than 0.5%.